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R Burattini

Publications and source records attributed to R Burattini.

18 recordsLinked to original sources
PubMed1992

Evaluation of hypercholesterol diet-induced changes in viscoelastic properties of carotid circulation in pigs.

Measurements of pulsatile pressure and flow at the input of the left and right carotid arteries and a new lumped parameter model were used to quantify changes in the overall dynamic mechanical properties of the carotid circulation between five control diet-fed pigs and five pigs fed a hyperlipidemic diet for 16 wk. The model represents the portion of the circulation supplied by either the left or the right carotid artery and is characterized by five parameters: peripheral resistance (Rp), an overall inertance (L), and an overall frequency-dependent compliance constituted by a capacitor C (static compliance) in series with a Maxwell section, i.e., a capacitor Cd, in parallel with a resistor Rd. Rp was calculated as the ratio between mean pressure (P) and mean flow (Q). The other four parameters were estimated by fitting measured to model predicted flows. The average static compliance was reduced by 40% (P = 0.01) between normal (P = 62.0 +/- 4.3 mmHg) and hyperlipidemic diet-fed pigs (P = 62.7 +/- 4.7 mmHg). A significant reduction in the overall cross-sectional area was inferred from a 53% increase (P = 0.05) in L, whereas resistance vessel tone was unchanged as judged from estimates of Rp. No signs of occlusive disease were found in any of the animals.

Animals↗
PubMed1991

Systemic autoregulation counteracts the carotid baroreflex.

The interaction between autoregulation and baroregulation and its effect on the gains of the short-term pressure regulatory system was studied by performing both open- and closed-loop experiments in the same five anesthetized, vagotomized dogs, and by analyzing the data making use of a new model. With carotid pressure constant (no baroregulation) the pressure-flow data were convex to the flow axis, thus indicating the presence of autoregulation. When baroregulation was present the data were convex to the pressure axis. Our model was able to fit the data as measured in both cases. From the fitting procedure the zero-flow pressure intercept Pzf, the autoregulation resistance gain Gra, and the baroregulation resistance gain Grb were estimated. Pzf was about 20 mmHg in three dogs and about zero in the other two. Average values of Gra and Grb were 13.0 +/- 3.5 mmHg min2/L2 and 0.83 +/- 0.25 min/L, respectively. The two curves which fitted the data points collected in the presence and in the absence of baroreflex intersected at a point (Qo, Po) generally different from the control point. We determined the open-loop gain, Goc = GrbQo, about the point (Qo, Po). The averaged value was 2.23 +/- 0.84. When autoregulation was neglected, the resistance gain Grb and the open-loop gain Goc obtained from the same closed-loop method were underestimated (0.32 +/- 0.15 min/L and 0.88 +/- 0.48, respectively). In the open-loop preparation the carotid sinuses were isolated and the aortic (P) versus carotid (Pca) pressure data were collected. A third-order polynomial was fitted to these data.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Two arterial effective reflecting sites may appear as one to the heart.

The relation between reflected waves and features of ascending aortic pressure waveforms and impedance patterns was investigated with a modified T-tube model of the systemic arterial circulation. Ascending aortic pressure and flow and descending aortic flow were measured in 10 dogs under basal conditions and under the effect of an agent (methoxamine) that caused vasoconstriction and an increase of mean aortic pressure. A broad range of aortic pressure amplitudes and features was obtained. These waveshapes were classified into four groups. Under basal conditions, cases for which a prominent diastolic fluctuation was present (n = 8) were grouped in A. Cases for which this fluctuation was absent (n = 2) were grouped in B. Groups C (n = 4) and D (n = 3) included cases that, under vasoconstricted conditions, did or did not display, respectively, a diastolic fluctuation in pressure. Arterial T-tube model parameters were estimated by simultaneously fitting the model to both ascending and descending aortic flow with aortic pressure as input. A good fit was obtained in any case considered. After parameter estimation, forward and reflected waves and impedance patterns at the entrance of head circulation (head and upper limbs) and body circulation (trunk and lower limbs) as well as their merger in the ascending aorta were determined. T-tube input impedance compared well with impedance data points obtained from the ratio of corresponding harmonics of ascending aortic pressure and flow. In some cases (group A), modulus and phase spectra displayed two distinct minima, in the range from 0 to 10 Hz. In some other circumstances, these minima were less distinct (groups B and C) and could even appear as one (group D). Whether one or two minima appeared in the ascending aortic impedance spectra at low frequency and whether a prominent diastolic fluctuation did or did not appear in aortic pressure, pressure and flow waveshapes proximal to the heart were explained by the presence of two effective reflecting sites in the systemic circulation. In group B, a diastolic fluctuation in pressure was absent despite the fact that head-end and body-end reflected waves were distinct. This happened because body-end reflected waves peaked corresponding to a minimum of the head-end reflected wave. In group D, a diastolic fluctuation in aortic pressure was absent because the body-end reflected wave moved into systole and superimposed on the head-end reflected wave. This superimposition was due to increased pulse wave velocity in the body transmission path as a result of decreased arterial distensibility.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Short-term systemic autoregulation.

We studied total systemic autoregulation in closed-chest, chloralose-anesthetized dogs. Cardiac out-put (previously implanted electromagnetic flow probe on ascending aorta) and aortic pressure were varied by reducing venous return using a balloon catheter in the vena cava. Compensatory action of the baroreflex was prevented by bilateral vagotomy and isolation of both carotid sinuses. To avoid high vessel tone carotid sinus pressure was set at the original baseline value using a pressurized blood reservoir. With each balloon inflation aortic flow and aortic pressure decreased and stabilized in about 1 min. Pressure and flow were allowed to return to base-line values after each balloon inflation in an attempt to minimize the activation of slower regulatory mechanisms. The steady-state pressure-flow relations could be fitted with a sigmoidal curve. The mean quality (0 less than Q less than 1) of autoregulation in eight dogs was 0.41 +/- 0.08 (SD). Autoregulation was found in the pressure range from 42 to 140 mmHg. The early appearance of total systemic autoregulation suggests that, in the intact animal, it may counteract baroreflex control.

Animals↗
PubMed1990

Time-domain formulation of asymmetric T-tube model of arterial system.

An asymmetric T-tube model of the arterial system with complex terminal loads was formulated in the time domain. The model was formulated to allow it to be fitted to the aortic pressure waveform, the aortic flow waveform, or simultaneously to both the aortic and descending aortic flow waveforms. Pressure and flow measurements were taken in anesthetized open-chest dogs under basal, vasoconstricted, and vasodilated states. It was found that the T-tube model fitted the data well in all formulations and in all vasoactive states. However, all parameters were estimated accurately in all vasoactive states only with the formulation that fitted to both aortic and descending aortic flow simultaneously. The T-tube model was compared with the three-element windkessel model with regard to the respective models' ability to recreate specific aspects of the pressure waveform and with regard to the estimates of global arterial parameters. The T-tube model recremated those features of the pressure waveform, such as diastolic waves, that the windkessel model could not. Also, the T-tube model systematically estimated lower global arterial compliance and higher characteristic impedance than the windkessel. It was argued that the T-tube model accurately represented important wave transmission features of the arterial loading system. The model is recommended for use in characterizing the arterial load and for merging with representations of the left ventricle in studies of left ventricle-systemic arterial interaction.

Animals↗
PubMed1989

Modified asymmetric T-tube model to infer arterial wave reflection at the aortic root.

A modified version of the T-tube model was constructed to represent the systemic arterial loading system as "seen" by the left ventricle (LV). This model consisted of two uniform tubes connected in parallel. It differs from the original T-tube model in that the transmission paths have no frictional losses and are terminated with complex impedances, rather than simple resistors. To estimate model parameters (load and tube compliances, tube inertances, characteristic impedances, and peripheral resistances) we measured ascending aortic pressure and flow in a group of five open-chest, anesthetized dogs. Parameter estimates were obtained by fitting experimental pressure to the pressure predicted by the model from experimental flow. To check the reliability of the model, an additional experiment was performed where flow in the upper descending thoracic aorta was measured in addition to ascending aorta pressure and flow. The fit between the experiment and model predicted ascending aortic pressure was satisfactory in all six dogs. This pressure was always characterized by the presence of a prominent diastolic oscillation. Our model showed that this oscillation is due to reflections from the lower body, the effective reflection site being most probably located at the level of middle to low abdominal aorta. The effective reflection site located in the upper body is closer to the heart. The related reflected wave affects pressure in late systole.

Analog-Digital Conversion↗
PubMed1987

Short-term regulation of arterial pressure and the calculation of open-loop gain in the intact anesthetized dog.

Open-loop gain of the short-term systemic pressure regulation was determined under closed-loop conditions in the closed chest anesthetized dog (n = 5). For this purpose, cardiac output and mean systemic pressure were varied by ventricular pacing after the production of complete heart block. From the pressure-flow data resistance gain (the ratio of peripheral resistance change to pressure change in the steady state) was obtained by means of a simple model. The value of this gain was automatically estimated by fitting the pressure-flow relation described by the model to the experimental data. The model allows the pressure-flow relation to be straight or curved with or without a zero-flow pressure intercept. The best fit was obtained when the pressure-flow curve was convex to the pressure axis and had no intercept. When the model was linearized about the control values of pressure and flow (operating point), open-loop gain could be calculated from resistance gain. Its averaged value in the control condition, 1.63 +/- 0.45, is in agreement with values found by other investigators in open-loop conditions. During vasoconstriction open-loop gain, at the (new) operating point, increased to 2.51 +/- 0.51; during vasodilation it decreased to 1.17 +/- 0.27. Open-loop gain about an operating point thus can be determined in the intact animal from measurements of mean pressure and mean flow in the steady state.

Animals↗
PubMed1987

Total systemic arterial compliance and aortic characteristic impedance in the dog as a function of pressure: a model based study.

Total arterial compliance and aortic characteristic impedance as a function of pressure in the anesthetized closed chest dog (n = 5) were studied. The three-element windkessel (consisting of a peripheral resistance, a total systemic arterial compliance, and an aortic characteristic impedance) was assumed as an arterial model. Aortic pressure was varied by pacing the heart at different rates after the production of atrioventricular block and by administration of Angiotensin and Hydralazine. Model parameters were estimated by two different methods. The first was based on a computerized optimization procedure using all the information contained in the aortic pressure and flow waveforms. The second method used the diastolic decay of aortic pressure to compute total arterial compliance and used the arterial input impedance spectrum to compute aortic characteristic impedance. Total arterial compliance and aortic characteristic impedance changed with pressure. The parameter optimization procedure yielded values of total arterial compliance ranging from 0.20 to 1.4 ml/mmHg and values of aortic characteristic impedance ranging from 0.05 to 0.42 mmHg sec/ml. Values of parameters estimated on the basis of the impedance spectrum and diastolic pressure decay were similar. Compliance values as a function of mean aortic pressure could be fitted with a bell-shaped curve similar to that found from in vitro studies of aortic segments. Characteristic impedance values as a function of mean aortic pressure could be fitted with a parabolic function the minimum of which was found in the range of control to high pressures (90-160 mmHg).

Animals↗
PubMed1985

Identification of canine coronary resistance and intramyocardial compliance on the basis of the waterfall model.

This study was performed to elucidate the effects of cardiac contraction on coronary pressure-flow relations. On the basis of the waterfall mechanism, a lumped model of the coronary arterial system is presented consisting of a proximal (epicardial) compliance, a coronary resistance, and an intramyocardial compliance. A "back"-pressure, assumed to be proportional (constant k) to left ventricular pressure, impedes flow. From steady-state measurements of circumflex coronary artery flow and inflow pressure, together with left ventricular pressure, the values of the three model parameters and the constant k have been estimated. In the control condition proximal compliance is found to be 1.7 X 10(-12) m4s2kg-1, intramyocardial compliance 110 X 10(-12)m4s2kg-1, and resistance 7.5 X 10(9) kgm-4s-1. The proportionality constant k is close to unity. Effects of changes in left ventricular pressure and inflow pressure and the effect of vasoactive drugs on the parameters are also investigated. Changes in coronary resistance are always opposite to changes in intramyocardial compliance. Sensitivity analysis showed that epicardial compliance plays its major role during isovolumic contraction and relaxation; resistance plays a role throughout the cardiac cycle but is more important in diastole than in systole, whereas intramyocardial compliance plays a role in systole and in early diastole.

Animals↗
PubMed1985

A simple algorithm for defining the mean cardiac cycle of aortic flow and pressure during steady state.

A fast procedure for defining a cardiac cycle using simultaneously recorded and digitized aortic flow and pressure is presented. A simple algorithm, based on a double-threshold method, initially involves singling the dicrotic notch of flow in order to separate contiguous cardiac cycles during a given steady state. The individual cycles are carried back to a common origin of time, then they are normalized to the mean length and averaged. As a result of an averaging operation the algorithm gives a "mean cycle" of both pulsatile aortic pressure and flow. An "a posteriori" analysis of the noise components in the data has been carried out in order to justify the averaging operation. The "mean cycle" of aortic flow and pressure are suitable to be used as the input quantities of the automatic identification procedures recently assessed to estimate the parameters of simple models of the arterial input impedance. Our algorithm was defined and implemented as a FORTRAN program for a digital PDP 11/24 computer. This algorithm was tested by using pressure and flow data measured in the ascending aorta of dogs. About 26 sec were necessary to select 10 cardiac cycles (each one being about 200 samples long) of both flow and pressure in sequences of 2500 samples per signal and to compute the respective "mean cycles." Total peripheral resistance, total arterial compliance, and aortic characteristic impedance were estimated by aid of the simple three-element windkessel model. The results obtained by our method of determining parameters on the "mean cycle" of aortic pressure and flow were compared to the results obtained by averaging the parameters determined on each heart cycle.

Animals↗
PubMed1984

Closed-loop baroreflex control of total peripheral resistance in the cat: identification of gains by aid of a model.

The baroreflex regulation of total peripheral resistance was quantified in closed-loop conditions. To vary arterial pressure cardiac output was reduced by graded inferior caval vein occlusion or by arterial bleeding. In eight lightly anaesthetised cats the static relation between mean arteriovenous pressure gradient and mean flow could be described by a curve that was convex to the pressure axis and had zero intercept. The ratio of the change in resistance to a given change in arterial pressure was taken as resistance gain (GR). The value of this gain was estimated with the aid of a model which predicts pressure from flow when the right parameter value for gain is filled in. It consists of a non-linear negative-feedback control system with control pressure as reference point and with a constant gain. The estimation was carried out with the aid of an automatic identification procedure. GR varied from 0.002 to 0.010 min . ml-1 in different animals under light anaesthesia. With deeper anaesthesia gain decreased by 35 to 50% and became zero with very deep anaesthesia or barodenervation. Assuming that the reflex is a linear system about control pressure and flow we linearised our model and computed the static overall open-loop gain (GO). Within this narrow range GO varied from 0.64 to 2.30 for different cats under light anaesthesia and decreased by the same percentage as GR with deeper anaesthesia.

Animals↗